The present invention relates to pressure swing adsorption (PSA) techniques for the separation of a preselected gas or gases from a gas mixture including said gas or gases.
PSA techniques are used in a wide variety of applications where it is desired to separate a particular gas, for example, oxygen or nitrogen from a gas mixture containing oxygen or nitrogen, for example, air.
PSA techniques are also used when it is desired to control or modify an atmosphere in a container. For example, many refrigerated containers utilise a modified atmosphere for the transportation of produce such as foodstuffs. Fruit and vegetables when transported in closed containers frequently give off carbon dioxide and ethylene, the levels of which have to be controlled if the produce is to be maintained in a fresh, edible state. Known PSA systems for controlling or modifying the atmosphere in a container are frequently bulky and difficult to service and repair. Bulk is a problem particularly when the container whose atmosphere is to be controlled forms part of a land vehicle such as a lorry where space is at a premium. Carbon dioxide control in modified atmosphere containers is known to be effected by the use of a chemical such as sodalime which adsorbs excess carbon dioxide. The arrangement is such that the level or percentage by volume of carbon dioxide in the container is monitored and when a preselected level is reached, a fan circulates the gas mixture in the container over the sodalime which adsorbs the carbon dioxide. This continues until a preselected level of the carbon dioxide in the gas mixture is reached after which the fan is shut down.
This arrangement is simple but has a number of limitations in particular the disposal of the spent sodalime and its replacement.
It is an aim of the present invention to provide a multi-bed PSA pressure vessel which is relatively compact and easy to assemble and disassemble.